1. Field
This disclosure relates generally to semiconductor device packaging, and more specifically, to forming a gel-filled cavity package having an overflow reservoir using film-assisted molding.
2. Related Art
Many of today's automobiles provide constant monitoring of the state of the vehicle for safety and informative purposes. One common monitoring feature found in many automobiles is a tire pressure monitoring system. Typically, pressure sensors coupled to transmitters are mounted in each wheel of the car. If the pressure of the tire drops below a predetermined value, a signal is transmitted from the pressure sensor and provided to a diagnostic information center of the vehicle.
A typical pressure sensor semiconductor device package can incorporate a microcontroller unit, a pressure sensing cell and one or more other sensors coupled to the microcontroller unit. The pressure sensing cell can be mounted in a cavity of a pre-molded plastic package having a lid with one or more holes allowing the ambient air pressure to enter the cavity. The pressure sensing cell is protected from contaminants in the ambient air (e.g., water, oil, or dirt), by a protective coating, such as a silicone gel, which is added to the cavity to cover both the pressure sensing cell and any exposed connections in the cavity. In order to stop the gel from creeping up to the lid/package attachment junction, sharp edged features are molded into the cavity wall.
The gel used to fill the cavity is relatively expensive. Since the size of the pre-molded package cavities is typically large, this results in significant additional production costs for the packaged pressure sensor devices. Further, the interface between a package lead frame and the pre-molded package material can trap air bubbles which can be released into the gel during ambient air pressure decrease events. These air bubbles can decrease the accuracy of the pressure sensor device and interfere with capacitive signal transmission within the package cavity.
It is therefore desirable to provide a cavity semiconductor device package that decreases the gel volume as well as decreases any opportunity for bubble formation. Such a cavity semiconductor device package should also provide for measures to stop any gel used to protect devices in the package from contacting the lid of the package or the lid/package attachment junction.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.